過濾器

攔截器的目的是想在做一些事前之前，處理一些動作，主要是思想，具體實現都是無所謂的

設計思想

• 攔截器可以採用連結串列或者陣列實現，這裡採用List
• doSomething這裡採用靜態代理，返回一個攔截器代理類，執行doSomething

簡單的程式碼實現

原操作類

public class Person {
	public void doSomeThing(String msg) {
		System.out.println("doSomeThing ，然後輸出資訊: " + msg);
	}
}

攔截器

public interface Intercepter {
	
	/**
	 * @param target 	原操作類
	 * @param args		方法引數
	 */
	void intercep(Object target, Object... args);
}

public class AuthIntercepter implements Intercepter {

	@Override
	public void intercep(Object target, Object... args) {
		if (target instanceof Person) {
			System.out.println("你有許可權操作 doSomething方法");
		} else {
			throw new RuntimeException("非法操作");
		}
	}
}

public class ArgsIsNullIntercepter implements Intercepter {

	@Override
	public void intercep(Object target, Object... args) {
		if (target instanceof Person) {
			Objects.requireNonNull(args);
			Objects.requireNonNull(args[0]); //doSomething有個msg引數
			System.out.println("引數校驗通過");
		} 
		
	}

}


public class OtherIntercepter implements Intercepter {

	@Override
	public void intercep(Object target, Object... args) {
		if (target instanceof Person) {
			System.out.println("攔截器要做一些處理");
		}
		
	}

}


public class OtherIntercepter implements Intercepter {

	@Override
	public void intercep(Object target, Object... args) {
		if (target instanceof Person) {
			System.out.println("攔截器要做一些處理");
		}
		
	}

}

 

攔截器代理類

public class PersonIntercepterProxy {

	// 攔截器佇列
	private List<Intercepter> intercepters = new ArrayList<Intercepter>(16);
	
	// 靜態代理
	private Person person;
	
	public PersonIntercepterProxy(Person person) {
		this.person = person;
	}
	
	public void registerIntercepter(Intercepter intercepter) {
		if (intercepter != null) {
			intercepters.add(intercepter);
		}
	}
	
	public void unRegisterIntercepter(Intercepter intercepter) {
		if (intercepter != null) {
			intercepters.remove(intercepter);
		}
	}
	
	public void doSomething(String msg) {
		// 先執行攔截器佇列
		for (Intercepter intercepter : intercepters) {
			intercepter.intercep(person, msg);
		}
		
		// 再執行原操作類
		person.doSomeThing(msg);
	}
}
 

測試

public class IntercepterTest {

	public static void main(String[] args) {
		// 原操作類
		Person person = new Person();
		// 攔截器代理類
		PersonIntercepterProxy proxy = new PersonIntercepterProxy(person);
		// 註冊攔截器
		proxy.registerIntercepter(new AuthIntercepter());
		proxy.registerIntercepter(new ArgsIsNullIntercepter());
		proxy.registerIntercepter(new OtherIntercepter());
		// doSomething
		proxy.doSomething(" hello 你好");
	}

}
 

測試結果

你有許可權操作 doSomething方法
引數校驗通過
攔截器要做一些處理
doSomeThing ，然後輸出資訊:  hello 你好

更改測試類

public class IntercepterTest {

	public static void main(String[] args) {
		// 原操作類
		Person person = new Person();
		// 攔截器代理類
		PersonIntercepterProxy proxy = new PersonIntercepterProxy(person);
		// 註冊攔截器
		proxy.registerIntercepter(new AuthIntercepter());
		proxy.registerIntercepter(new ArgsIsNullIntercepter());
		proxy.registerIntercepter(new OtherIntercepter());
		// doSomething
		proxy.doSomething(null);
	}

}

測試結果

你有許可權操作 doSomething方法
Exception in thread "main" java.lang.NullPointerException
	at java.util.Objects.requireNonNull(Unknown Source)
	at demo.impl.ArgsIsNullIntercepter.intercep(ArgsIsNullIntercepter.java:14)
	at demo.PersonIntercepterProxy.doSomething(PersonIntercepterProxy.java:33)
	at demo.IntercepterTest.main(IntercepterTest.java:19)